Laboratory Diagnosis of Peste des Petits Ruminants (PPR): Diagnostic Tools and Their Applications

Peste des Petits Ruminants (PPR) remains one of the most economically significant viral diseases affecting sheep and goats. The disease is characterized by high fever, erosive stomatitis, respiratory involvement, and severe diarrhea, with mortality reaching up to 90% in susceptible populations¹. While clinical signs often raise suspicion, they may vary in severity and overlap with other infectious diseases, making laboratory confirmation an essential part of disease diagnosis and control^2,3. 

Why Laboratory Confirmation Matters 

Clinical findings alone may not always distinguish PPR from conditions such as Foot and Mouth Disease, bluetongue, capripox, contagious ecthyma, pneumonic pasteurellosis, or caprine pleuropneumonia. Some infected animals may also fail to exhibit the complete spectrum of clinical signs, increasing the likelihood of misdiagnosis. In such situations, laboratory testing provides the definitive diagnosis needed for timely disease control measures¹. 

An effective diagnostic approach involves selecting appropriate laboratory tests based on the purpose of investigation, available facilities, and the stage of disease. 

Virus Isolation: The Reference Method 

Virus isolation remains the gold standard for confirming PPR virus infection. Isolation is commonly performed using Vero cells, where characteristic cytopathic changes, including cell rounding, grape-like cell clusters, vacuolation, cytoplasmic granulation, and syncytia formation, typically develop within three to five days of infection⁴. 

Despite its diagnostic value, virus isolation is not routinely used in many laboratories because it is time-consuming, requires specialized cell culture facilities, and is less sensitive than RT-PCR⁵. 

Serological Tests 

Several serological techniques continue to play an important role in PPR diagnosis and surveillance. 

Agar gel immunodiffusion (AGID) and indirect ELISA have traditionally been used for primary diagnosis. However, cross-reactions between PPR and rinderpest antibodies reduce their specificity. Competitive ELISA offers greater sensitivity and specificity than AGID and remains useful even when samples have not been optimally preserved⁵. 

Sandwich ELISA (s-ELISA) provides high diagnostic performance, with reported sensitivity of 99.8% and specificity of 90.5%, making it useful for detecting PPR virus in nasal and ocular secretions^4,5,6. 

Virus Neutralization Test (VNT) serves as the prescribed assay for international trade and is particularly valuable as a confirmatory test for differentiating PPR from rinderpest while detecting PPR antibodies in serum samples^4,5. 

Hemagglutination assay (HA) offers a rapid, simple, inexpensive, and reliable confirmatory option with greater sensitivity than AGID, making it suitable where quick laboratory confirmation is required⁴. 

Molecular Diagnostic Techniques 

Molecular assays have become increasingly valuable because conventional serological methods can be labour-intensive and less sensitive during primary diagnosis. 

Real-time RT-PCR enables rapid and highly sensitive detection of viral RNA from clinical samples and overcomes many limitations associated with conventional assays⁵. 

Multiplex RT-PCR further improves diagnostic capability by amplifying multiple target genes simultaneously, reducing false-negative results that may occur because of RNA degradation, primer binding alterations, or PCR inhibitors. Single-step multiplex assays also reduce the risk of cross-contamination and allow simultaneous detection of several important respiratory pathogens affecting sheep and goats^4,7. 

Loop-mediated isothermal amplification (LAMP) demonstrates even higher sensitivity than RT-PCR while minimizing sample contamination. Its simplicity makes it particularly suitable for laboratories with limited financial resources⁸. 

Practical Clinical Insights 

Selecting the appropriate diagnostic test depends on the clinical situation, laboratory infrastructure, and the objective of testing. Virus isolation remains the reference method but is impractical for routine diagnosis. Serological assays continue to support surveillance and antibody detection, whereas molecular techniques provide rapid, sensitive confirmation during suspected outbreaks. Combining clinical evaluation with timely laboratory confirmation strengthens disease surveillance, supports effective control programmes, and enables earlier implementation of preventive measures when PPR is suspected.

References 

1. Kwiatek O, Ali YH, Saeed IK, Khalafalla AI, Mohamed OI, Obeida AA, Abdelrahman MB, Osman HM, Taha KM, Abbas Z, El Harrak M. Asian lineage of peste des petits ruminants virus, Africa. Emerging infectious diseases. 2011 Jul;17(7):1223. https://pmc.ncbi.nlm.nih.gov/articles/PMC3381390/pdf/10-1216_finalR.pdf 

2. Balamurugan V, Hemadri D, Gajendragad MR, Singh RK, Rahman H. Diagnosis and control of peste des petits ruminants: a comprehensive review. Virusdisease. 2014 Jan;25(1):39-56. https://pmc.ncbi.nlm.nih.gov/articles/PMC3889233/pdf/13337_2013_Article_188.pdf 

3. Kinimi E, Odongo S, Muyldermans S, Kock R, Misinzo G. Paradigm shift in the diagnosis of peste des petits ruminants: scoping review. Acta Veterinaria Scandinavica. 2020 Jan 29;62(1):7. https://link.springer.com/content/pdf/10.1186/s13028-020-0505-x.pdf 

4. Mahmoud MA, Ghazy AA, Shaapan RM. Diagnosis and Control of Peste des Petits Ruminants Disease in Small Ruminants: A Review. World's Veterinary Journal. 2022;12(2):214-20. https://cyberleninka.ru/article/n/diagnosis-and-control-of-peste-des-petits-ruminants-disease-in-small-ruminants-a-review 

5. Santhamani R, Singh RP, Njeumi F. Peste des petits ruminants diagnosis and diagnostic tools at a glance: perspectives on global control and eradication. Archives of virology. 2016 Nov;161(11):2953-67. https://doi.org/10.1007/s00705-016-3009-2 

6. Mahajan S, Mohapatra JK, Pandey LK, Sharma GK, Pattnaik B. Truncated recombinant non-structural protein 2C-based indirect ELISA for FMD sero-surveillance. Journal of virological methods. 2013 Nov 1;193(2):405-14. http://dx.doi.org/10.1016/j.jviromet.2013.07.003 

7. Settypalli TB, Lamien CE, Spergser J, Lelenta M, Wade A, Gelaye E, Loitsch A, Minoungou G, Thiaucourt F, Diallo A. One-step multiplex RT-qPCR assay for the detection of Peste des petits ruminants virus, Capripoxvirus, Pasteurella multocida and Mycoplasma capricolum subspecies (ssp.) capripneumoniae. PLoS One. 2016 Apr 28;11(4):e0153688. https://journals.plos.org/plosone/article/file?id=10.1371/journal.pone.0153688&type=printable 

8. Venkatesan G, Bhanuprakash V, Balamurugan V. Development and comparative evaluation of loop mediated isothermal amplification (LAMP) assay for simple visual detection of orf virus in sheep and goats. Molecular and cellular probes. 2015 Jun 1;29(3):193-5. https://www.academia.edu/download/53194029/Development_and_comparative_evaluation_o20170519-7310-9ecxp1.pdf